Process of cracking of hydrocarbons such as for the production of high grade so-called antiknock motor fuel



March 15, 1938. H. c. PENNRICH PROCESS OF CRACKING OF HYDROCARBONS SUCH AS FOR THE PRODUCTION E SO-CALLED ANTIKNOCK MOTOR FUEL OF HIGH GRAD Filed Feb. 26, 1955 FT-esh Feed Gas Gasoline Tar sr H Id Sfora e Sfora e 2 gag-swing I Vaporizer 5 lsf -cl a/ 1 Hearing l:' E: Zane 3 8 Crack/n9 Henry C. Pennn'ch.

' INVENTOR.

Zone

ATTORNEYS.

Patented Mar. 15, 1938 rnocnss or CRACKING F nrnnocnnnous soon AS FOR THE PRODUCTION or HIGH GRADE SO-CALLED MOTOR FUEL ANTIKNOGK" Henry 0. Pennrich, Brussels, Belgium Application February 26, 1935, Serial No. 8,274

2 Claims.

.This invention relates to the process of cracking large molecular hydrocarbons under high pressure for the production of smaller molecular hydrocarbons such as are present in highgrad 5 so-called antiknock motor fuel.

My process is distinguishedfrom those of the the absence of coke formation, the possibility of fractionating in any desired ratio and .the sim-' plicity of equipment as well as the possibility of easily converting existing apparatus of the conventional type to make them suitable for the carrying out. of my process. Other advantages are low cost of production and saving of fuel as can be recognized from the disclosed process.

It is the experience of those engaged in this art, that in the carrying out of cracking processes, as they are known to-day, there is formation of undesirable products along with the ,use-

iul and desirable products through which the yield in useful products is diminished or the process may be interrupted. Thus the formation of coke and carbon depositsmay clog the apparatus and interrupt the process and instead or the desirable gasoline other-products suchas hydrocarbon gases are produced in large quantities. It has always been the desire of those enthe formation of these undesirable products.

It is known in this art that the power generated by a motor fuel increases with thepossibility of high compression in the cylinder of the motor and the production of cracked gasoline witha high compression stability or of so-called antiknock qualities has become highly important. Processes known as vapor-phase cracking processes were developed for the production of motor fuel with distinct antiknock properties. These vapor-phase cracking processes, operating at pressures of below 100 pounds per square inch and at temperatures of around 1000 F., are however, characterized by the production of larger quantities of gas and more coke for a given amount of charging stock than previous cracking processes known as liquid-phase cracking processes. The danger of coke formation in these processes is so great, that to obtain a low coke formation, only light distillates such as kero sane and light gasoil can be cracked by this process. Through the recognizing of certain improvements, I have overcome the difliculties of the formation of coke and the" production of excesgaged in this art to be able to avoid or to diminish sive gas quantities while still obtaining a high octane number-gasoline; thus in practice they are found to be ofgreat value. I

It is proven by experience that the reaction of crackingdepends upon the temperature (2011- ditions during which the conversion takes place. The best conditions are toraise the temperature of the products instantly to the required optimum cracking temperature, to keep the temperature then constant for the required length of time and to lower the. temperature rapidly at the end of the reaction.

I have recognized that heavy g'asoilsand fuel oils can becracked without cokeformation when a reaction time of ten- (10) minutes or over is used and means are provided to prevent overheating. The temperature reached under these conditions must be the optimum cracking temperature. A sudden increase in the production of gas and the beginning of coke formation start when the temperature in the cracking unit rises considerably above the optimum cracking tem-' perature. In many of the cracking processes, as they are practiced today, the products are heated to a temperature considerably above the optimum cracking temperature, either before they enter or while they are in the cracking zone. Then cooling takes place during the reactionand the temperature of the mixture drops below. the optimum cracking temperature. I found that near the walls of the tubes 9. temperature often 100 F. higher than the average temperature of the products undergoing the reaction exists. The temperature then drops due partly to losses by radiation but mainly due to the absorption of heat incident with the cracking. Temperature drops of 50 F. and more are experienced in these cracking zones. v By overcoming thesedefects in the cracking process, I have found that both qualitatively and quantitatively the resulting yields of gasoline are very materially increased. To avoid the conditions outlined consists in providing means' which prevent the temperature to deviate from the optimum cracking temperature, 1. e. either to increase or decrease substantially" from the optimum cracking temperature during the time in which the cracking reaction takes place and further to provide means by which the reaction time can be readily controlled.

This is accomplished by passing the preheated products 1 to be cracked under high pressure through tubes, -placed into a moderately heated furnace and adding hydrocarbon vapors prohydrocarbons of the kerosene, gasoil and fuel-,

duced in the process and boiling below the boiling point of gasoline, which have been heated under high pressure to temperatures above the optimum cracking temperature of the oil to be cracked. They are fed into the stream of the products to be converted and also the heated vapors are entered into the conversion unit at various points.

It is known in this art that hydrocarbon gases are useful as heat carriers in cracking processes.

In some vapor-phase cracking processes, a hydrocarbon gas heated to about 1100 F. is mixed with r a light gasoil vapor heated to about 950 F. in

proportions to give a temperature of about 1000" F. in the mixture. The mixture is passed through a nonheated vessel in which it remains for a reaction time of less than .1 second. Pressures of below 100 pounds per square inch are used. The disadvantages of these operations were outlined'above.

It is also known that high pressure in cracking is a favorable factor, as it improves heat transfer conditions and aids in preventing overheating. Increased pressure gives also decreased gas Thus crude oil productsor crude oils are charged into a flash tower from which heavy tar is periodically withdrawn. The overhead vapors are fractionated into a hydrocarbon gas, a gasoline and a distillate. The distillate contains oil type. The-distillate is heated under pressure to a temperature at which cracking will not take place. The hydrocarbon gas, part of which is being continuously withdrawn, is heated under pressure to a temperature above the cracking temperature of the distillate, and part of the oleflnic hydrocarbonspresent in the gas oil will. undergo a reaction of condensation forming higher boiling cyclic hydrocarbons.

The preheated distillate and the one part of heated ,gas are introduced into a tubular reaction zone, the quantity of the gas being so controlled that the optimum cracking temperature of the distillate results instantaneously. A rapid mixing of both streams is secured. by passing it through a nozzle in which the pressure is lowered by about 25 pounds. The reaction starts immediately and being endothermic, it absorbs heat. The absorbed heat is resupplied by aciding further quantities oi'the heated gas at various points into the cracking zone. The losses of heat by radiation are prevented by placing the tubular cracking unit into a furnace which is moderately heated.

When the reaction hasprogressed to the end after a cracking time of ten (10). minutes or more, the reaction is rapidly terminated by lowering the pressure and admixing.colder products such as are to be cracked later on and whereby they are heated. The mixture is then passed into a flash tower for the separation of the tar and then into a fractionating tower.

In this way, I accomplish various desirable functions, which are rapid heating and cooling, the conversion under high pressure at a constant temperature of high molecular weight hydrocarbons, removing by fractionation any of the desired products and recycling products desired for further conversion, prevention of coke formation and the production of the highest possible yields of gasoline with high 'antiknock characteristics.

One typical example of the application of this process is described in detail in the followin process. 1

The fresh feed such as crude mineral oil products obtained from crude mineral oils, tars or similar materials, is stored in a tank I, from which by means of, pump 2 it is passed through the heat exchangers 3- and 4. Thus preheated to a temperature of around 350 F., the feed is mixed at point 5 with the products emerging from the cracking zone, whereby the temperature of the cracked products is rapidly lowered to about 750 F. and the cracking-reaction is suddenly brought to a stop.

The mixture of fresh feed and of cracked products is passed into a vaporizer 6 which is heat insulated-and maintained at a deflnite temperature by refluxing oil from the bottom of a fractionating tower III by means of the reflux pump ll and'the reflux line II. The pressure of this tower is around pounds per square inch. A heavy t r, collecting at the bottom of the vaporizer, either continuously or periodically withdrawn and passed through the heat exchanger and the cooler I into the storage tank 8.

The vapors leaving the vaporizer are partly cooled in the heat exchanger 0 and enter the fractionating tower l0. The temperature of this tower is controlled by gasoline reflux taken from the receiving vessel It by means of ,the reflux pump 22 and the reflux line 23. A temperature of about 330 F. prevails at the top and a temperature .of about 540 F. prevails at the bottom of the tower which operates at a pressure of about 25 pounds per square inch. Distillates at various temperatures can be taken oil. In this example only two products are taken. The vapors pass through the heat exchangers 3 and ii, the cooler l1 and they enterthe receiving drum It. The gasoline leaving the bottom of the receiving drum is sent into the, gasoline or storage tank It. Part of the cracked gas leaving the top of the receiving drum is sent into the gas holder 20. The other part of the gas is passed through the gas scrubber 2| in which corrosive products such as hydrogen sulphide are removed. The purified gas is heated in the heat exchangers l6 and 0. compressed to a pressure ofabout 1000 pounds per square inch and picked up by the high pressure pump 24. By means of the control valves 25 and 26 the gas is divided into two streams and passed through a. number of tubes placed in the furnace 21. The temperature of the gas is raised to about 1050" E, during this the oleflnic hydrocarbons present in the gas are converted into gasoline rich in cyclic hydrocarbons.

The high boiling condensate leaving the bottom of the fractionating tower i0 is aspirated by the high pressure pump it and compressed to a pressure of about 1000 pounds per square inch. The compressed condensate is passed into the tubular heating zone ll placed in the furnace ii. The oil is here heated to atemperature at which substantial cracking will not take place which is around 800 F. The oil thus preheated issent to the craclnng zone 02 placed in the furnace 30. The cracmng zone consists of a (the nozzle is not shown).

number of tubes with a diameter of around three inches. At point 20, before entering the crack I of about 860 to 080 F. instantaneously results in the mixture. The cracking reactionistarts and absorbs heat. an additional quantity of the heated gas is therefore in reduced into the cracmng zone at point 20. Heat losses by radia tion are prevented by moderate heating of the furnace 30. The length of the tubes is so adjusted'that a reaction time of 10 utes or more is obtained and the reaction time is also controlled by increasing or decreasing the amounts of heated gas introduced at point 29. A pressure 01' around 980 pounds per square inch is maintained in the cracking zone by means of the pressure controlvalve 3i.

The cracked products, leaving the reaction zone with a temperature of around 860 to 800 F. are decreased in pressure by the valve 3! and is usually found advantageous topreheat the oil.

mixed with the fresh feed at point 5, whereby the temperature is quickly decreased 'and'the reaction brought to a stop.

The temperatures given above are for illustration purposes only; they may vary within reasonable limits for-different charging stocks. The temperature of the oil lea the preheating zone i0 may range between 700 and 800? F; but diflerences between the temperatures of the products entering the cracking zone and v the products leaving the cracking zone should not exceed F. The temperature to which the gas is heated before entering the cracking zone 02 may be somewhat above or below 1050" F.

It is not required that the pressure must be maintained at around '1000 wunds per square.

inch. 'The pressure may vary considerably between 300 and 3000 pounds per square inch. It

and the gas at pressures oi 10 to 15 pounds above t those used in the cracmng zone. In the vaporizer and the fractionating tower, pressures of below 50 pounds per square inch are found sat factory,

o be understood that of three different furnaces as shown in the drawing, only two or even one-may be used it by proper combination or design the above outlined tern-- perature conditions can be secured. Having thusdescribed one typical example of my process, I do not bind myself to the exact details given in the above description, but rather consider this as one example illustrating the with crac products, passing the mixture to a vag zone and separating vapors and gases from unvaporized liquid, fractionating the over.- head products to obtain non-condensed gases, a motor fuel and a condensate, passing said condensate'at a pressure of above300 pounds per square inch through a. heating zone and heating it to a temperature of below 800 F., heating non-condensed gases at the same pressure to a temperature of about 1050 R, passing. the mixture through an outside heated tubular cracking zone of such length that the reaction time is at least 10 minutes, introducing additional heated non-condensedgases to keep the temperature of the mixture constant until said condensate is cracked, mixing the cracked products with cooler fresh charge oil to bring the temperature of the mixture below 800 F. and passing the from unvaporized liquid, traction'ating the overhead products to obtain non-condensed gases, a motor fuel and a condensate, passing said candensate at a pressure of above 300 pounds per square inch through a heating zone and heating it to a temperature of about 800 E, heating nonoondensed gases at approximately the same pressure to a temperature of about 1050 F., mimng a part of the heated gases with the heated oil and passing the mixture through a cracking zone a in which. a reaction time of at least ten minutes is obtained, introducing additional heated non condensed gases to keep the temperature of the mixture 'const until part of the condensate is cracked, mixing the cracked products with cooler charge oil to bring "the temperature of the mixture to below 800 52,- and passing the mixture into said capo-zone.

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